This invention relates to the production of acid soluble humic acids by sulfoalkylation of humic acid bearing ores. Production by the sulfoalkylation process described herein gives humic acids which have better solubility in acid systems and which are different from humic acids produced by earlier processes.
One such earlier process for producing humic acids is described in U.S. Pat. No. 5,004,831. The process involves mixing oxidized coal with aqueous alkali, heating the mixture to 100.degree. to 180.degree. C. under sufficient pressure to prevent evaporation of water, and maintaining the elevated temperature for a time sufficient to extract a substantial amount of the available humic acids. While this process produces humic acids in high yields, the humic acids thus produced are not sulfomethylated and have poor acid solubility.
The process disclosed herein also produces humic acids which are superior to those produced by traditional methods. These traditional methods for producing humic acids from humic acid bearing ores involve extraction with alkali. An example of such an extraction process is described in U.S. Pat. No. 4,319,041. It involves mixing humic acid containing ores with water and caustic soda and extraction of the humic acids by agitation at pH 6.5-8.0. The times required in this process are quite lengthy, however, and the humic acids produced are not acid soluble.
A method for producing sulfonated humic acids is described in U.S. Pat. No. 4,502,868. In it, SO.sub.2 is used as the sulfonating agent. The sulfonated humic acid salts produced are claimed to be good viscosity reducers for coal water slurries. Under the conditions employed in the process, however, sulfonation is not sufficient to give solubility in low pH fertilizers.
Zhambal (Khim Tverd. Tolp. (Moscow) 1991, (2), 70-2) has also shown that humic acids can be sulfonated by reaction with concentrated sulfuric acids. During this process, however, the material is not solubilized in the acid. Thus the products formed would not have good solubility in low pH fertilizers.
A third method for sulfonating humic acids is described by Sharanova et al (Khim Tverd. Topl. (Moscow) 1987, (3), 38-43). In this method sulfonation is achieved by reaction of humic acids with sodium sulfite. However, since the products produced in the reaction are isolated by precipitation in dilute acid, it is clear that this method does not sulfonate sufficiently for solubility in low pH fertilizers.
Similarly, a method for producing sulfonated humic acids by reaction of humic acid bearing ores at low pH with a mixture of sodium sulfite and sodium bisulfite is described in Spanish Patent ES 495,426. Like the products described above, however, the products produced by this method can be isolated by precipitation in strong acids, and therefore, would have poor solubility in low pH fertilizers.
Pobedonostseva, et al (Khim. Tverd. Topl. (Moscow) 1978, (6), 97-102) describes a two step process for producing sulfomethylated lignite drilling mud thinners. In this process, humic acid is extracted from brown coals with alkali, and the resulting humic acids are sulfomethylated to make the final drilling mud thinners. While sulfomethylated humic acids are produced in the process, two separate steps are required. Additionally, there is no mention given to the levels of sulfonation required for solubility of the humic acids in acid fertilizers.